See also

When Apache starts, it binds to some port and address on
the local machine and waits for incoming requests. By default,
it listens to all addresses on the machine. However, it needs to
be told to listen on specific ports, or to listen on only selected
addresses, or a combination. This is often combined with the
Virtual Host feature which determines how Apache responds to
different IP addresses, hostnames and ports.

The Listen
directive tells the server to accept
incoming requests only on the specified port or
address-and-port combinations. If only a port number is
specified in the Listen
directive, the server
listens to the given port on all interfaces. If an IP address
is given as well as a port, the server will listen on the given
port and interface. Multiple Listen directives may be used to
specify a number of addresses and ports to listen on. The
server will respond to requests from any of the listed
addresses and ports.

For example, to make the server accept connections on both
port 80 and port 8000, use:

Listen 80
Listen 8000

To make the server accept connections on two specified
interfaces and port numbers, use

Listen 192.170.2.1:80
Listen 192.170.2.5:8000

IPv6 addresses must be surrounded in square brackets, as in the
following example:

A growing number of platforms implement IPv6, and APR supports
IPv6 on most of these platforms, allowing Apache to allocate IPv6
sockets and handle requests which were sent over IPv6.

One complicating factor for Apache administrators is whether or
not an IPv6 socket can handle both IPv4 connections and IPv6
connections. Handling IPv4 connections with an IPv6 socket uses
IPv4-mapped IPv6 addresses, which are allowed by default on most
platforms but are disallowed by default on FreeBSD, NetBSD, and
OpenBSD in order to match the system-wide policy on those
platforms. But even on systems where it is disallowed by default, a
special configure parameter can change this behavior
for Apache.

If you want Apache to handle IPv4 and IPv6 connections with a
minimum of sockets, which requires using IPv4-mapped IPv6 addresses,
specify the --enable-v4-mappedconfigure
option and use generic Listen
directives like the following:

Listen 80

With --enable-v4-mapped, the Listen directives in the
default configuration file created by Apache will use this form.
--enable-v4-mapped is the default on all platforms but
FreeBSD, NetBSD, and OpenBSD, so this is probably how your Apache was
built.

If you want Apache to handle IPv4 connections only, regardless of
what your platform and APR will support, specify an IPv4 address on all
Listen directives, as in the
following examples:

Listen 0.0.0.0:80
Listen 192.170.2.1:80

If you want Apache to handle IPv4 and IPv6 connections on separate
sockets (i.e., to disable IPv4-mapped addresses), specify the
--disable-v4-mappedconfigure option and
use specific Listen directives like the following:

Listen [::]:80
Listen 0.0.0.0:80

With --disable-v4-mapped, the Listen directives in the
default configuration file created by Apache will use this form.
--disable-v4-mapped is the default on FreeBSD, NetBSD, and
OpenBSD.

Listen does not implement
Virtual Hosts. It only tells the main server what addresses and ports to
listen to. If no <VirtualHost> directives are used, the server will behave
the same for all accepted requests. However,
<VirtualHost>
can be used to specify a different behavior
for one or more of the addresses and ports. To implement a
VirtualHost, the server must first be told to listen to the
address and port to be used. Then a
<VirtualHost> section
should be created for a specified address and port to set the
behavior of this virtual host. Note that if the
<VirtualHost>
is set for an address and port that the
server is not listening to, it cannot be accessed.